“Time flies like an arrow; fruit flies like a banana.”
It’s a phrase loved by linguists to show how
a sentence can be read in multiple ways. It also holds truth about the common
fruit fly, Drosophila melanogaster,
which has been studied by scientists for more than 100 years
Fruit flies do like bananas. They are the flies you find
on your fruit bowl when things start to rot – a reminder that the
"five-a-day" hasn’t been going quite so well.
But they are also a great mechanism for
studying time or, more specifically, the effects of time because fruit flies'
life cycle is so fast, it allows scientists to study them over generations that
would be near-impossible with humans.
They are cheap to breed and reproduce extremely quickly.
At room temperature a female can lay 30-50 eggs per day throughout her lifetime
and they have a short reproductive cycle, usually about 8-14 days and can
become grandparents in only 3-4 weeks.
At 3mm in size, populations in the millions
can be kept in the lab at any one time and fed on a simple diet of
carbohydrates and protein, usually cornmeal and yeast extract.
This creature, which most of us brush aside,
has been responsible for some of the greatest discoveries in modern science.
In 1933, Thomas Hunt Morgan won a Nobel Prize for
studying how Drosophila inherited a genetic mutation that
meant they had white eyes rather than red. His research led to a theory that
genes made by DNA were carried on chromosomes, which were passed down through
generations. The finding laid the groundwork for the study of genetic
inheritance and modern genetics.
Since then research carried out on Drosophila
has led to five Nobel laureates in 1946, 1995 and 2011. Current thinking on how
we develop, our behaviour, ageing and evolution are all built on the foundation
of fruit fly research. The more we study them the more similar we discover we
are: 75% of human disease genes have a recognisable match in the common fruit
fly.
Drosophila has four pairs of chromosomes and
around 14,000 genes. Compare that with humans, which have an estimated 22,500,
and yeast, which has about 5,800 genes, and we are much more similar than you
might expect.
This relative genetic closeness means experiments onDrosophila translate effectively to humans and
scientists. We get them drunk to study alcohol addiction, we study sleep and
how they are affected by coffee and we have learned that older flies sleep
less. The first ‘jet lag genes’ were found in flies, and we now know we have
them too.
Thousands of scientists use Drosophila as a model organism across all of the
world, even outside it. Fruit flies were the first animals launched into space
and there is a permanent Fruit Fly Lab on the International Space Station. This
is used to study questions such as why astronauts are more susceptible to
disease when in space.
Why then, if we are genetically close are we
different in so many ways to the fruit fly or even yeast? Dr Peter Lawrence,
author of The Making of the Fly, describes this as the "third secret of
life".
In an interview for the BBC
Radio 4 series Natural Historieshe said the first secret is
Charles Darwin’s theory of evolution, which “drives the genesis of all the
plants and animals, everything, from scratch”.
“The second is the discovery of DNA because
without understanding that information is coded and stored in this molecule
then we wouldn’t have much of an understanding of a mechanism that lies behind
life,” he said.
The third secret is a question Dr Lawrence
sees as the greatest problem that must be tackled by the biologists of the
future.
“It is so every day that we don’t think about
it. What makes the difference between a rhino and hippo?” he said.
“When you look at the genes, it’s not much. So, what
makes the pattern and the size and so on? Where is the length of your nose
specified and what information present when you are developing fixes it at a
particular length? What makes children resemble their parents, what makes the
shape of a face? We actually don’t know.
“That for me is the biggest unsolved problem
in biology and is what I call the ‘third secret of life’. You see it every day
but it is so big it’s not obvious how to approach it.”
“You can’t build an animal without vectorial
information so we need to know where a cell is, what it is and where it’s
pointing. Imagine an architect’s plans without any orientation of north or
south you wouldn’t know which way to put the building.”
It’s a subject scientists have tried to break down. Flies
with larger wings have been studied to try to isolate the genes responsible for
the increase in size. Scientists have compared species that are evolutionarily
closely related and tried to examine the differences that lead to differences
in their morphology.
But, according to Dr Lawrence, these studies
are valuable in contributing pieces in a puzzle but there is long way to go
before we answer the big question and we need to make it a greater focus of
scientific study.
“If you look at the whole cosmos of science
you see a big dark area, space, and if you look more closely you see that, here
and there, there are many rooms full of light and in each there are people all
beavering away and arguing and discussing with one another but they don’t look
out of the windows and see and wonder what there might be out there.”
Whatever the answers are, Dr Lawrence says,
the chances are that they will be found by studying Drosophila.
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